This invention relates to a chloride process for producing TiO.sub.2 by addition of an inert gas in a vapor phase oxidation of TiCl.sub.4 and more particularly, to a process for controlling TiO.sub.2 agglomeration by addition of the inert gas into a reaction zone where the TiO.sub.2 particles are formed.
U.S. Pat. No. 4,574,078 and related U.S. Pat. Nos. 4,24 1,042 disclose addition of an inert gas as a carrier gas and diluent in a process to hydrolyze volatile titanium compounds. Therein, the inert gas is added before reaction of the volatile titanium compound with steam. No mention is made of using an inert gas to control particle size and/or agglomeration of the TiO.sub.2.
A chloride process for producing TiO.sub.2 pigment by reacting O.sub.2- containing gas and TiCI.sub.4 at temperatures ranging from 900.degree. to 1600.degree. C. in a vapor phase is known. The resulting hot gaseous suspension of TiO.sub.2 particles and free chlorine is discharged from the reactor and must be quickly cooled below 600.degree. C. within about 5 to 100 seconds. This cooling is accomplished in a conduit, i.e., a flue so that undesired TiO.sub.2 particle size growth is prevented and particle agglomeration is minimized. Pigment product properties such as carbon black undertone (CBU) and gloss are a function of primary particle size and particle agglomeration, respectively. If high agglomeration of TiO.sub.2 results, the TiO.sub.2 must be milled or ground in an energy intensive, expensive process such as micronizing to reduce the size of agglomerates in order to achieve the desired pigment properties.
The chloride process described above, however, produces TiO.sub.2 with variable agglomeration as production rate changes. The need therefore exists for a solution to maintain the degree of agglomeration as constant as possible. The degree of agglomeration changes also according to size and design of cooling flues. There is need to maintain a given level of agglomeration if larger diameter flues are used as these might lead to reduced agglomeration on account of reduced turbulence. The present invention meets those needs.